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I was wondering how to safely convert a Hybrid GPT/MBR to a pure GPT partition scheme? (Without Reformatting)

The reason why I ask is, I currently triple-boot with Ubuntu 16.04 LTS, Windows 10 and Mac OSX Lion.

Originally I needed to format my drive with a Hybrid partition scheme to install Windows 7 but I have since upgraded to Windows 10.

I know now that Windows 10 supports booting from GPT partitions and I would like to covert everything to a pure GPT partition scheme without reformatting.

If I can do this, I would be able to reformat my HFS+ partition to an APFS partition and install High Sierra.

So the questions are:

  1. How do I convert my Hybrid MBR to a pure GPT?
  2. Will it break booting into any of my OSes if I do? (Windows 10, Linux, MacOSX)

Here is my gdisk output:

GPT fdisk (gdisk) version 1.0.1

Partition table scan:
  MBR: hybrid
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with hybrid MBR; using GPT.

Command (? for help): p
Disk /dev/sda: 3907029168 sectors, 1.8 TiB
Logical sector size: 512 bytes
Disk identifier (GUID): CBC86EEB-C878-4C46-9963-120433EB0BED
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 3907029134
Partitions will be aligned on 8-sector boundaries
Total free space is 269477 sectors (131.6 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              40          409639   200.0 MiB   EF02  EFI System Partition
   2          409640       293378391   139.7 GiB   AF00  Mac OSX
   3       293642240       684265471   186.3 GiB   0700  WINDOWS 7
   4       684265472      1075085311   186.4 GiB   0700  LINUX
   5      1075085865      1087375589   5.9 GiB     8200  
   6      1087375590      3907024064   1.3 TiB     0700  
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From the gdisk(8) manual:

n – Create a new protective MBR. Use this option if the current protective MBR is damaged in a way that gdisk doesn't automatically detect and correct, or if you want to convert a hybrid MBR into a "pure" GPT with a conventional protective MBR.

You need to enter the experts’ menu to access this option.

  1. Open the drive in gdisk:

    sudo gdisk /dev/sdX
    
  2. Enter the experts’ menu (x).

  3. Create a new protective MBR (n) and answer any dialogue questions as suitable.

  4. Return to the main menu (m).

  5. Write the changes to the drive and exit gdisk (w).

You may need to reinstall Grub in EFI mode if it was installed in MBR mode before.

| improve this answer | |
  • I think I will continue using it as a Hybrid MBR/GPT setup since there are no clear answers on whether it will work and what sort of pitfalls there are. My intent is simply to reformat the HFS+ partition and do a clean install of High Sierra. Lastly, Is it safe to simply reformat the HFS+ partition only without breaking anything? (Correct me if I am wrong, I think I may have to resync my Hybrid MBR with gdisk after installing High Sierra) – coolcatco888 Jul 23 '18 at 5:33
  • @coolcatco888: You can save the entire current partition table with gdisk (b in the main menu), make the above (or any) changes, see what happens and restore the partition table to its previous state with gdisk again (l in the recovery & transformation sub-menu). – David Foerster Jul 23 '18 at 9:14
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In my opinion the only way that you can convert Hybrid MBR to pure GPT is to reformat the drive that you want to convert because as soon as you install your OSes on Hybrid MBR, it writes data on the drive, hence, I don't think there is a application or a way to do it. Because you basically mess up with the bootloader file for Windows, Ubuntu and Mac

I hope I can answer your question.

Would you mind let me know what mac are you using right now?

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  • I'm using OSX Lion right now but as of this afternoon, I installed clover as my bootloader and now I cannot boot into it. – coolcatco888 Jul 22 '18 at 6:19
  • Actually, could you know if it is safe to reformat just the MacOSX partition? If so, would I also be able to reformat it as a APFS partition? – coolcatco888 Jul 22 '18 at 6:20
  • @coolcatco888 I think that the only solution for your problem is that you can either stick with what you have right now or do a backup for your files in all OSes then do a fresh reinstall and format the drive as GPT. And I don't think you should reformat the OS partition because you can accidentally delete your bootloader. – Aaron Pham Jul 23 '18 at 3:46
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It works as described. In fact I was able to restore broken APFS Volume on a hybrid partition. You need to have knowledge of the layout of the partitioning. For more info see this post: https://apple.stackexchange.com/questions/390955/apfs-partition-inaccessible/391012#391012

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